1. Field of the Invention
The present invention relates generally to a filter for purifying various liquids containing magnetic particles, such as fuels, lubricants, and cooling liquids among others. Specifically, the invention relates to filters employing internal magnetic elements to trap such magnetic particles. The filter of the present invention can be used with particular success as a disposable fuel or oil filter for a device with limited energy resources such as an internal combustion engine.
2. Description of the prior art
Filtration of liquids has been widely described in the prior art. In addition to other contaminants, some liquids contain particles that are magnetic in nature. For the purposes of this description, a magnetic particle is defined as a small (generally less then 0.01 of an inch in diameter) particle that can be attracted and retained on the surface of such known permanent magnets as defined by a chemical formula of SrFe.sub.12 O.sub.19, or BaFe.sub.12 O.sub.19. Most of these magnetic particles fall in one of two categories: ferromagnetic particles such as Fe, Co, Ni, other metals and metal alloys as well as ferrimagnetic such as magnetic oxides Fe.sub.3 O.sub.4, .gamma.-Fe.sub.2 O.sub.3, various ferrites, CrO.sub.2 and alike.
Two particularly useful areas of filtration in which the present invention can be used most advantageously are the filtration of fuels such as gasoline, kerosine, diesel and alike as well as filtration of lubricants such as various oils.
Fluid filters are generally capable of removing contaminants having particle sizes above a given minimum size, while smaller particles pass through the filter medium. A balance must be struck between the lower size limit of retained particles and the flow rate allowed by the filter, because as the filter medium is constructed to retain smaller particles, the speed with which fluid flows through the medium is reduced. Therefore, it is simply not possible to remove all contaminants at practical rates of flow.
Metallic contaminants cause particular concern, because they may be very small, yet cause damage to the mechanism the filter is intended to protect. In, for example, an automotive engine, it is very important to remove minute metallic contaminants from the circulating lubricating oil to prevent damage to the internal engine components. Additionally, normal engine operation continually causes the production of additional metallic contaminants. The filter medium necessary to retain such metallic contaminants would cause excessive back pressure, and therefore, these fine metallic contaminants must be removed by another means.
It is also known that the majority of contaminating particles contain both magnetic elements such as metals as well as non-magnetic elements such as metal oxides. In fact, as metal particles enter the circulating liquid they undergo an oxidation process becoming less magnetic. Oxide particles are extremely hard and therefore particularly abrasive and damaging to an engine. Therefore, retaining both magnetic and partially magnetic particles is an important objective of a magnetic filter.
One alternative means of removing fine metallic particles from the fluid passing through the filter is to include a magnetic element in the filter that attracts and traps the metallic contaminants that exhibit magnetic attraction, such as iron, steel and their oxides, either before or after they pass through the filter medium. Various attempts have been made to incorporate a magnetic component in a filter.
Prior art magnetic filters that have included a magnetic element have generally done so by including some type of a bar magnet inside the filter assembly. For example, U.S. Pat. No. 3,279,607 by Michaelson discloses an automotive oil filter having one or more bar magnets disposed in one or more folds of the filter material, spaced equally around the circumference of the filter housing. Similarly, U.S. Pat. No. 4,501,660 by Hebert relates to an oil filter having a magnetized helical coil disposed in the central core of the filter assembly. An externally-attached magnetic element is disclosed by U.S. Pat. No. 5,282,963 by Hull, et al. A magnetic element sized to fit over the end of an oil filter housing is attached to the filter housing by magnetic attraction to metallic elements of the housing and filter. Similarly, U.S. Pat. No. 5,354,462 by Perritt relates to a strap that fastens around the outside of an oil filter housing to hold in place magnetic elements. U.S. Pat. No. 2,893,561 by Duzich relates to sheets of filter element material having small particles of magnetic material dispersed throughout the material or attached to the surface by impregnating the sheet with a polyvinyl acetate bonding agent.
These and other filters have inherent disadvantages, either in that they complicate the manufacturing process, cause increased back-pressure, or in that the magnetic elements are not optimally designed and placed relative to the fluid flow path so as to maximize the fluid contact with the magnetic element, and hence the removal of magnetically-attractive contaminants. Also, separately acting individual magnets do not produce strong enough magnetic field throughout the filter since the force that attracts a particle to a magnet falls off inversely proportional to the third degree of the distance from the center of magnet. Therefore, magnetic "blind spots" are inherently associated with the filters of the prior art.
Other attempts have been made to produce magnetic filters to remove some or all of the metallic and especially abrasive partially metallic particles circulating in the lubricating oil due to the normal wear occurring in an internal combustion engine or similarly to remove magnetic particles from the fuel fed into that engine.
U.S. Pat. No. 2,915,185 by Waldherr is directed to a fuel filter comprising an air dome and magnetic filter for automotive fuel pump lines, in which a magnet is provided in the dome in the path of the fuel. The fuel thus flows past the magnet and when the magnet becomes loaded with magnetic particles, there is a tendency for a surge of fuel to sweep away the collected particles, often in highly concentrated surges. Also such filters and domes are permanently connected to the engine, and thus have to be regularly dismantled, cleaned and reassembled as a periodical service.
A further fuel filter is shown in U.S. Pat. No. 2,914,178 by J. L. Edelen in which a magnet is positioned to allow the fuel to flow over the magnet, which also allows the particles to be swept away by the flood of fuel.
U.S. Pat. No. 3,186,549 by Botstiber, shows a permanent filter including magnetic filtration in which the liquid flows over the magnet and in which an indicating device is incorporated to give a signal when the filter is clogged or loaded. However, some collected particles could be swept away before the indication is given.
U.S. Pat. No. 2,823,803 by Sinclair et al, shows a permanent magnetic filter with a relatively expensive magnet forming a circular array of pole pieces which co-operate with a plurality of soft iron rods. The permanent magnet can be partially rotated to reverse the polarity of the soft iron rods to dislodge the attracted magnetic particles which fall into a lower chamber for collection.
U.S. Pat. No. 2,317,774 by Kiek et al, shows a permanent filter which allows attraction of magnetic material in the oil in an air gap outside the flow path, but this is a permanent type of filter which has to be serviced.
U.S. Pat. Nos. 1,778,910, 2,014,800, 2,392,624, 2,429,920, 2,721,659, 2,860,787, 2,980,257, 3,127,255, 3,421,627, 3,841,489, 3,887,469, 3,979,288, 4,036,758, 4,053,410, 4,261,815, 4,295,969, 4,298,478, 4,363,729, 4,366,065, 4,450,075, 4,629,558, 4,663,029, 4,759,842, 4,865,730, 5,174,892, and 5,568,869 all disclose various forms of magnetic devices for attracting magnetic materials from fluid (usually lubricating oil or fuel). These filters in general have to be dismantled for cleaning, washing, possible replacement of filter elements, and reassembled, care being taken that all seals and sealing rings are correctly sealed so that no leakage occurs. Also with the magnetic elements disclosed, it is believed that these are not entirely satisfactory in removing most of the magnetic materials. Additionally, the present trend is to increase the ease of servicing oil and fuel filters by making them disposable whereby it is merely necessary for the filter to be removed and disposed and a new filter installed.
As it is also well known, the surface tension of liquids and fuels in particular can be considerably decreased under the influence of treating with a strong magnetic gradient. As a consequence of reduced surface tension, dissolution and mixing of different additives admixed to the liquid, as well as atomizing properties increase to a significant extent. Increased atomizing properties are considered as most advantageous with respect to fuels.
In view of the fact that the nozzles and atomizers of pumps of oil-heated equipment are most sensitive and the cost of regeneration of the feeders and atomizers of internal combustion motors is extremely high, apparatus is needed which can reduce or eliminate harmful effects of abrasive particles having magnetic properties.
Treating with a magnetic field is most important not only in the case of fuels, but it was observed that when water was treated with a magnetic field damaging scale deposition could be reduced or completely avoided on the walls of fittings and pipes in contact with the water. Another known use of a water treated with a strong magnetic field is in production of stronger concrete.
Additional area of utilization of the filter of the present invention is for purifying a fluid containing magnetic particles and more particularly for purifying the cooling fluids of water cooled nuclear reactors. In pressurized water reactors, the pressurized water, which constitutes the primary fluid and which comes into contact with the fuel rods before being sent into the steam generators in order to heat and vaporize, the boiler feed water or secondary fluid, becomes charged, during its circulation in the reactor and in the steam generators, with iron oxide particles formed during the prolonged contact of the water with certain steel parts of the nuclear reactor.
In boiling water reactors, the water in the main circuit comes into contact with the fuel rods and vaporizes. The steam thus produced feeds the turbine. The condensed water becomes charged with particles in the water tank. The water is reintroduced into the reactor and circulates by means of circulating pumps. The oxide particles tend to become activated and to deposit on the fuel assemblies when vaporization takes place. It is very important to remove these oxide particles from the fluid by means of a filter, in order to prevent the amount of oxide in this fluid from becoming excessive and to prevent these particles from becoming activated after having resided in the core and from depositing on the components, making a significant contribution to the activity and to the contamination of the surfaces. This purification of the fluid must of course be carried out while the reactor is in operation in order to ensure continuous purification of the water.
In order to effect this purification, it has been proposed to use an electromagnetic filter comprising a cylindrical envelope filled with beads of a ferromagnetic material, and more particularly steel beads, which are subjected to a magnetization cycle so that these beads can retain the magnetic particles conveyed by the fluid. A filter of this type, which comprises a magnetizing device surrounding the cylindrical envelope in which the beads are located, in order to create a magnetic field capable of magnetizing the beads, is generally arranged in parallel with a pump used for the circulation of the water. An example of this filter can be found in the U.S. Pat. No. 4,304,667 by Dubourg. The design is extremely complex and requires constant reversal of magnetization process.
Therefore, the need exists for a magnetic filter with a simple preferably disposable design capable of removing magnetic particles from a liquid without creating a significant back pressure but at the same time providing high level of purification.